Ultrasonic diagnostic method and an ultrasonic diagnostic apparatus for carrying out the same

ABSTRACT

An ultrasonic diagnostic method and apparatus are provided for enhancing real-time performance, enlarging visual field, and improving S/N ratio without sacrificing any of real-time performance, visual field and S/N ratio by field into two or more sections; generating sounding waves forming a main lobe and grating lobes to scan the sections of the visual field respectively by the main lobe and the grating lobes; separately and directively processing an echo wave received along the direction of the main lobe and echo waves received along the directions of the grating lobes to form images of the sections separately; and combining the images of the sections to display an image of the visual field.

TECHNICAL FIELD

The present invention relates to an ultrasonic diagnostic method and anultrasonic diagnostic apparatus and, more specifically, to an ultrasonicdiagnostic method that employs grating lobes to enhance real-timeperformance, to enlarge visual field and to improve S/N ratio, and anultrasonic diagnostic apparatus for carrying out the ultrasonicdiagnostic method.

BACKGROUND ART

In carrying out Doppler color flow mapping (CFM) by the conventionalultrasonic diagnostic apparatus, the pitch p of oscillatory elements andthe wavelength λ of an ultrasonic sounding wave are determined so as tomeet an inequality, p<λ/2 so that only a main lobe exists in the visualfield, i.e., so that no grating lobe exists in the visual field, and thevisual field is scanned by the main lobe.

The grating lobe is prevented from existing in the visual field toprevent formation of a virtual image by the grating lobe.

Although not directly related to the present invention, because thegrating lobe is different from the side lobe, a technique of preventinga virtual image attributable to the side lobe is disclosed in JapanesePatent Laid-open (Kokai) No. 61-11030.

In the Doppler CFM by the ultrasonic diagnostic apparatus, the real-timeperformance can be enhanced by increasing the frame rate F, the visualfield can be enlarged by increasing the number N of sound rays, and theS/N ratio can be improved by increasing the pulse repetition frequencyP.

However, since the relation between the frame rate F, the number N ofsound rays, the pulse repetition frequency (the number of successivepulses to cause the phase variation of one sound ray) P, the maximumdetection depth Dmax and the sound velocity c is expressed by:F×N×P×2D_(max) /c<1, the increase of the frame rate F, the increase ofthe number N of sound rays, and the increase of the pulse repetitionfrequency P contradict each other.

Accordingly, the enhancement of the real-time performance, the expansionof the visual field or the improvement of the S/N ratio, entailsinevitably the sacrifice of the visual field or the S/N ratio, thereal-time performance or the S/N ratio, or the real time performance orthe visual field.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide anultrasonic diagnostic method capable of enhancing real-time performance,enlarging visual field and improving S/N ratio without sacrificing anyof real-time performance, visual field and S/N ratio, and to provide anultrasonic diagnostic apparatus for carrying out the ultrasonicdiagnostic method.

In a first aspect of the present invention, an ultrasonic diagnosticmethod comprises; dividing a visual field into two or more sections;generating sounding waves forming a main lobe and grating lobes to scanthe sections of the visual field respectively by the main lobe and thegrating lobes; separately processing an echo wave received along thedirection of the main lobe and echo waves received along the directionsof the grating lobes to form images of the sections separately; andcombining the images of the sections to display an image of the visualfield.

In a second aspect of the present invention, an ultrasonic diagnosticapparatus comprises: an ultrasonic probe; a transmission control meansfor making the ultrasonic probe generate sounding waves forming a mainlobe and grating lobes and scan two or more sections of a visual fieldby the main lobe and the grating lobes, respectively; a main lobereceiving and processing means having a directivity only in thedirection of the main lobe and capable of forming an image of thesection scanned by the main lobe; a grating lobe receiving andprocessing means having directivities only in the directions of thegrating lobes and capable of forming images of the sections scanned bythe grating lobes; and an image display means for combining the image ofthe section scanned by the main lobe and the images of the sectionsscanned by the grating lobes and displaying an image of the visualfield.

The ultrasonic diagnostic method and the ultrasonic diagnostic apparatusin accordance with the present invention utilize positively the gratinglobes, which have been regarded as disturbances, from grating lobes inthe visual field to scan the sections of the visual field (onesection/one grating lobe) and scan only one section by the main lobe.The main lobe and the grating lobes are processed separately to formimages of the sections, and an image of the visual field is producedfrom images of the sections in a stage of display.

Since the areas of the sections are smaller than that of the visualfield, the number N of sound rays can be reduced without reducing thesound ray density and, consequently, the frame rate F can be increasedand the pulse repetition frequency P can be increased; that is, thereal-time performance can be enhanced and the S/N ratio can be improvedwithout sacrificing the visual field, or the number N of sound rays canbe increased without changing the frame rate F and the pulse repetitionfrequency P, which enables the expansion of the visual field.

Accordingly, generally, the real-time performance can be enhanced, thevisual field can be enhanced, and the S/N ratio can be improved withoutsacrificing any of the real-time performance, the visual field, and theS/N ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an ultrasonic CFM apparatus in a preferredembodiment according to the present invention;

FIG. 2 is a diagrammatic view helpful in explaining a main lobe, a firstgrating lobe, and a second grating lobe in a wave sending mode;

FIG. 3 is a diagrammatic view helpful in explaining a section allocatedto a first grating lobe in a wave receiving mode;

FIG. 4 is a diagrammatic view helpful in explaining a section allocatedto a main lobe in a wave receiving mode; and

FIG. 5 is a diagrammatic view helpful in explaining a section allocatedto a second grating lobe in a wave receiving mode.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment in accordance with the present invention will bedescribed hereinafter with reference to the accompanying drawings. Thepresent invention may be embodied in different forms without departingfrom the scope thereof and, therefore, the present embodiment isillustrative and not restrictive.

FIG. 1 is a block diagram showing the constitution of an ultrasonic CFMapparatus 1 in a preferred embodiment according to the presentinvention.

The ultrasonic CFM apparatus comprises an ultrasonic probe 2, atransmission control circuit 4, a receiving and processing circuit 7,and an image display circuit 17.

The ultrasonic probe 2 has an array of, for example, 128 oscillatoryelements 3 arranged at a pitch p of, for example, 0.21 mm. The centerfrequency is 3.5 MHz. Sound wave velocity in a medium through whichsound waves are propagated is 1540 m/s.

When all the oscillatory elements 3 send out sounding waves having awavelength of, for example, 0.44 mm, the relation expressed by p<λ/2 issatisfied, only a main lobe exists in the visual field, and no gratinglobe exists in the visual field.

When every third oscillatory element 3 sends out a sounding wave, theactual pitch P of the oscillatory elements 3 is, for example, 0.84 mm,which is four times the pitch p. Therefore, P>λ/2 when the wavelength 2of the wave is 0.44 mm and, as shown in FIG. 2, a first grating lobe GL1and a second grating lobe GL2 are formed respectively on the oppositesides of a main lobe ML at an angle of 30° to the main lobe ML.Supposing that the angular range of the visual field is 90°, both themain lobe and the grating lobes exist in the visual field.

When the oscillatory elements 3 are divided into groups 53 each of thefour successive oscillatory elements 3, and the oscillation of the foursuccessive oscillatory elements 3 is delayed properly relative to eachother so that the group is nondirectional, the oscillatory elements 3 ofeach group 53 function virtually as a single oscillatory element and,consequently, the operation of the ultrasonic probe 2 is equivalent tothat of the same in the foregoing mode in which only every thirdoscillatory element 3 sends out a sounding wave, and a main lobe andgrating lobes are formed in the visual field.

The transmission control circuit 4 comprises a sounding wave drivingcircuit 5 that generates transmission pulses, and a transmission delaycircuit 6 that delays the transmission pulses.

The transmission control circuit 4 drives every several oscillatoryelements 3 or delays the operation of the oscillatory elements 3 so thatthe plurality of oscillatory elements 3 function virtually as a singleoscillatory element to form a main lobe and grating lobes in the visualfield. Furthermore, the operation of the oscillatory elements 3 isdelayed for steering to make the main lobe and the grating lobes scansections of the visual field, respectively. For example, as shown inFIG. 2, a section K1 is allocated to the first grating lobe GL1, asection KM is allocated to the main lobe ML and a section K2 isallocated to the second grating lobe GL2.

The receiving and processing circuit 7 comprises preamplifiers 8,focusing delay circuits 9, first grating lobe extracting delay circuits10, main lobe extracting delay circuits 11, second grating lobeextracting delay circuits 12, a first grating lobe adder 14, a main lobeadder 15, and a second grating lobe adder 16.

The first grating lobe extracting delay circuits 10 are connected withall the oscillatory elements 3, respectively. A delay is determined sothat the oscillatory elements have a directivity in the direction of thefirst grating lobe GL1 shown in FIG. 2. The first grating lobe adder 14adds up the outputs of all the first grating lobe extracting delaycircuit 10. Thus, as shown in FIG. 3, a CFM image G1 (FIG. 1) of thesection K1 is formed.

Similarly, as shown in FIG. 4, the main lobe extracting delay circuits11 and the main lobe adder 15 form a CFM image G2 (FIG. 1) of thesection KM.

Similarly, as shown in FIG. 5, the second grating lobe extracting delaycircuits 12 and the second grating lobe adder 16 form a CFM image G3(FIG. 1) of the section K2.

The image display circuit 17 combines the CFM image G1 of the sectionK1, the CFM image G2 of the section KM and the CFM image G3 of thesection K2 to compose an image as shown in FIG. 1, and displays thecomposed image on a screen.

The ultrasonic CFM apparatus 1 scans the sections of the visual fieldrespectively by the lobes GL1, ML and GL2, and hence each lobe scans anarea 1/3 times an area to be scanned by the lobe by the conventionalultrasonic diagnostic apparatus. Therefore, the number N of sound rayscan be reduced without reducing the sound ray density and, consequently,the frame rate F can be increased and the pulse repetition frequency Pcan be increased; that is, the real-time performance can be enhanced andthe S/N ratio can be improved without sacrificing the visual field.

It is also possible to increase the number N of sound rays that can beincreased without changing the frame rate F and the pulse repetitionfrequency P to enlarge the visual field.

The ultrasonic diagnostic apparatus in accordance with the presentinvention is capable of achieving the enhancement of the real-timeperformance, the expansion of the visual field, and the improvement ofthe S/N ratio without sacrificing any of the real-time performance, thevisual field, and the S/N ratio.

I claim:
 1. An ultrasonic diagnostic method comprising the stepsofdividing a visual field into a plurality of sections; transmittingsound waves to form a main lobe and a pair of grating lobes, with themain lobe located between the pair of grating lobes, and to scan theplurality of sections, respectively, by the main lobe and the pair ofgrating lobes; separately processing echo waves received along thedirection of the main lobe and echo waves received along the directionsof the pair of grating lobes, thereby to form separate images of therespective sections for the received echo waves; and selectivelycombining the resulting separate images of the respective sections toproduce a combined image of the entire visual field, whereby real timeperformance is improved, visual field is enlarged and signal to noiseratio is improved.
 2. An ultrasonic diagnostic apparatus comprising:anultrasonic probe; a transmission control means for causing theultrasonic probe to generate sound waves forming a main lobe and a pairof grating lobes, with the main lobe located between the pair of gratinglobes, and for causing the main lobe and the pair of grating lobes toscan respective sections of a visual field; a main lobe receiving andprocessing means for receiving echo waves in a direction of the mainlobe and for processing the echo waves to form an image of the sectionscanned by the main lobe; a grating lobe receiving and processing meansfor receiving echo waves in directions of the pair of grating lobes, andfor processing the echo waves to form images of the sections scanned bythe pair of grating lobes; and an image display means for selectivelycombining the resulting images of the respective sections scanned by themain lobe and the pair of grating lobes to form a combined image of theentire visual field, and for displaying the combined image of the entirevisual field, whereby real time performance is improved, visual field isenlarged and signal to noise ratio is improved.